My favorites are ones which list the most relevant pages it can find (catching scenarios where URLs have changed but no redirect has been added) but only if the site has a functional search feature.

The problem is too many search libraries on sites are anywhere from useless to completely broken, even for some household name brand sites. My go-to test is while on an existing product page to search for either some part of the product title or a snippet of bullet point feature verbatim, to see if the page I'm currently on gets returned at all. It's stunning how many sites fail this test.